Many gas turbine engines use a heat exchanger or recuperator to increase the operating efficiency of the engine by extracting heat from the exhaust gas and preheating the intake air. Typically, a recuperator for a gas turbine engine must be capable of operating at temperatures of between about 500.degree. C. and 700.degree. C. internal pressures of between approximately 450 kPa and 1400 kPa under operating conditions involving repeated starting and stopping cycles.
Such circular recuperators include a core which is commonly constructed of a plurality of relatively thin flat sheets having an angled or corrugated spacer fixedly attached therebetween. The sheets are joined into cells and sealed at opposite sides and form passages between the sheets. These cells are stacked or rolled and form alternative air cells and hot exhaust cells. Compressed discharged air from a compressor of the engine passes through the air cells while hot exhaust gas flows through alternate cells. The exhaust gas heats the sheets and the spacers and the compressor discharged air is heated by conduction from the sheets and spacers.
An example of such a recuperator is disclosed in U.S. Pat. No. 3,285,326 issued to L. R. Wosika on Nov. 15, 1966. In such a system, the recuperator includes a pair of relatively thin flat plates spaced from an axis and wound about the axis with a corrugated spacer therebetween. The air flow enters one end and exits the opposite end, and the exhaust flow is counter-flow to the air flow entering and exiting at the respective opposite ends.
Another example of such a recuperator is disclosed in U.S. Pat. No. 3,507,115 issued to L. R. Wosika on July 28, 1967. In such a system, the recuperator comprises a hollow cylindrical inner shell and a concentric outer shell separated by a convoluted separator sheet which is wound over and around several corrugated sheets forming a series of corrugated air cores and combustion gas cores. In order to increase the transfer between the hot gases or cold air, the corrugated sheets are metallically bonded to the separator sheets in an attempt to increase efficiency. One of the problems with such a system is its lack of efficiency and the ability to test or inspect individual passages prior to assembly into a finished heat exchanger. Furthermore, the concentric outer shell is exposed to the recuperator temperatures on one side and to the environmental temperature on the other side. Thus, as the recuperator expands and contracts due to start up and shut down, the thermal stress and strain induced in the core at the point of connection between the convoluted separator sheets, the corrugated sheets and the concentric outer shell will be greatly varied and reduce the longevity of the structure.
Another example of such a recuperator is disclosed in U.S. Pat. No. 3,255,818 issued to Paul E. Beam, Jr et al, on June 14, 1966. In such a system, a simple plate construction includes an inner cylindrical casing and an outer annular casing having a common axis. Radially disposed plates form passages A and B which alternately flow a cooler fluid and a hotter fluid. A corrugated plate being progressively narrower in width toward the heat exchanger axis is positioned in the passage A, and a corrugated plate being progressively increasing in width toward the axis is positioned in the passage B. One of the problems with such a system is its lack of efficiency. Furthermore, the outer annular casing is exposed to the recuperator temperatures on one side and to the environmental temperature on the other side. Thus, as the recuperator expands and contracts due to start up and shut down, the thermal stress and strain induced in the core at the point of connection between the radially disposed plates and the outer casing will be greatly varied and reduce the longevity of the structure.
Another example of a circular recuperator or regenerator is disclosed in U.S. Pat. No. 3,476,174 issued to R. W. Guernsey et al, on Nov. 4, 1969. In such system, a radial flow regenerator includes a plurality of heat transfer segments formed by a number of laid-up thin corrugated sheet metal strips or shims. The segments are mounted between stiffeners, and a bridge is positioned in notches and secured to the segments. Thus, the regenerator, while providing a radial flow, fails to efficiently make use of the entire heat exchange area. For example, the stiffeners and bridges are positioned in an area which could be used for heat transferring purposes. Furthermore, the cost and complexity of the structure is greatly increased because of the notches and complex shapes of the control beams.
Another example of a heat exchanger construction is disclosed in U.S. Pat. No. 3,759,323 issued to Harry J. Dawson et al, on Sept. 18, 1973. A primary surface plate-type heat exchanger construction is shown and uses a plurality of flat successively stacked sheets having a plurality of edge bars for spacing the sheets apart. A large number of sheets are stacked in pairs with the edge bars therebetween to form a heat exchange core of a desired size.
The present invention is directed to overcome one or more of the problems as set forth above.